Abrasive article containing hollow spherules filled with lubricant



E. L. BARATTO ABRASIVE ARTICLE CONTAINING HOLLOW SPHERULES March 24,1970 3,502,453

FILLED WITH LUBRICANT Original Filed Aug. 9, 1965 IN VENT OR. 50 5/? L.63424 rro United States Patent Int. Cl. B24d 3/00 US. Cl. 51-295 8Claims ABSTRACT OF THE DISCLOSURE An abrasive article containing amultiplicity of separately prepared hollow spherules filled with alubricant.

The spherules rupture under grinding conditions and release thelubricant.

This application is a continuation of application Ser. No. 478,043,filed Aug. 9, 1965, and now abandoned.

This invention relates to abrasive articles such as coated abrasivesheet material, grinding wheels, and the like.

A perennial problem in any abrading, sanding, or grinding operation isthe generation of heat. This problem is particularly acute when theworkpiece being finished is metal which may distort or which is requiredto have a uniform attractive appearance. The generation of excess heatcauses buckling, discoloration, and, in some instances, destruction ofthe temper of the workpiece. For many years, it has been common tosupply a grinding aid, such as a lubricating oil, to the surface of theabrasive article, thereby reducing the frictional heat and increasingthe ease of cut. Although this technique is sometimes satisfactory, itis inconvenient, messy, requires additional equip ment and may create afire hazard.

The prior art discloses many attempts to include grinding aids within anabrasive structure. For example, US. Patent No. 2,327,846 suggests thatchlorinated hydrobon filler can be included in a grinding wheel, thefiller decomposing to form acidic metal-reactive substances during theabrading operation. Likewise, nearly half a century ago it was known(cf. US. Patent 1,325,503) to impregnate a porous grinding wheel withmolten paraflin, grease, oil, wax, or fat. Chlorinated naphthalenes havebeen similarly used; cf. US. Patent 1,900,430. Although each of thesetechniques is sometimes effective, highly acidic or corrosive grindingaids may also corrode the equipment on which they are used. In abradingoperations, a grinding wheel often gets so hot that much of theparafiin, wax, or similar filler material melts and is spun off beforethe wheel is consumed. US. Patent 2,734,812 suggests soaking particlesof expanded perlite in lubricating oil and including them in a phenolicresin bond. Not only does the lubricating oil tend to reduce theadhesion of the resin for the abrasive grains, but the oil also tends toseep prematurely from the wheel during storage.

The present invention provides a simple and convenient way of makingabrasive articles which contain grinding aids or lubricants and whichare extremely useful in sanding operations where generation of heat is aproblem. Grinding aids which are not receptive to the adhesive whichbonds the abrasive grains may be used, and far more grinding aid may beincluded than was ever before possible. Products can be made to possesswidely varied performance characteristics, and results are closelyreproducible. Resin-bonded wheels made according to my invention may bedesigned to run cool throughout their useful abrading life while stillretaining the ability to be run at high speed with superior rate of cutwhich distinguishes 3,502,453 Patented Mar. 24, 1970 them fromvitreous-bonded wheels. The products do not weep during storage, even atelevated temperatures.

In accordance with my invention I prepare abrasive products in whichgrinding aids are encapsulated in minute shells, typically hollowspherules, which maintain their integrity under normal handlingconditions but which rupture under grinding conditions. I have foundthat in some conditions as little as 1% by volume of the abrasivearticle (including abrasive grains) produces a noticeable improvement inabrading efficiency, while up to 25% is desirable under certain otheroperating conditions; generally speaking, the abrasion of regularworkpieces requires more lubricant than the abrasion of sharp or jaggedworkpieces.

The lubricant-containing capsules which I employ may be distributedthroughout the bond adhesive in a grinding wheel or in at least thesandsize of a conventional coated abrasive structure. One product inwhich my invention is effectively embodied is the abrasive wheel shownin Nestor U.S. Patent No. 2,862,806. The Nestor device is acircumferentially uniform accurately balanced molded abrasive articlecomprising a permanent hardened resinous annulus. The radially outerportion of the annulus is filled to a relatively substantial depth withabrasive grains, while the radially inner portion of the annulus may bedevoid of grains. I prefer to distribute encapsulated grinding aids onlyin the portion of the annulus actually containing abrasive grains.

The lubricant-filled spherules themselves may be formed from eitherorganic or inorganic materials, as will be shown. Ethyl cellulose,carboxymethylcellulose, polymers of methyl methacrylate, styrene,divinyl benzene, ethyl acrylate, methyl acrylate, or vinyl acetategelatin, gum arabic, starch, sugar, casein, alginates, pectin, Irishmoss, styrene-divinyl benzene copolymers, glass, ceramics, and metalsall maybe employed under appropriate conditions. The term lubricant isintended to embrace any nonabrasive substance which reduces either theforce required to cut metal, the tendency of freshly exposed metalsurfaces to weld to the abrasive grains, or both. Among substances foundto function effectively as lubricants in steel grinding are petroleumoil, chlorinated hydrocarbons, iron pyrites, parafiin, and divalentsulfur compounds. For grinding or sanding such other metals as zinc oraluminum, strongly acidic or basic materials (e.g., NaHSO, or NaOH) maybe employed as lubricants, a possibility which never before existed.Even wheels made with corrosive grinding aids of this type are perfectlysafe to handle but release controlled amounts of grinding aid. at thesite of stock removal.

Lubricants may be enclosed in spherules by any of several knownprocedures, simple coacervation, as described in US. Patent 2,800,458being suitable. In this process a hydrophilic colloid such as gelatin isdispersed in water, lubricant oil added, and the mixture agitated toform an oil-in-water emulsion. A coacervating salt is then added todecrease solubility of the colloid and cause it to form a fluid sheatharound the oil droplets. The temperature is then lowered to solidify thecolloid, and the resultant capsules washed and filtered. By varying therelative amounts of colloid and oil and the size of the oil droplets,one can produce capsules with a predetermined wall thickness. Speakingbroadly, the thinner the wall and/or the larger the capsule, the morereadily the capsule will be ruptured during grinding conditions.Capsules having a diameter much below 5 microns tend to resist fractureunduly and to contain insufficient lubricant to be commerciallyattractive. Likewise, capsules having a diameter in excess of 500microns tend to be hard to handle, often rupturing prematurely.

Lubricants may also be enclosed in capsules by other techniques. Forexample, a low molecular weight monomer may be dissolved in oil, whichin turn is dispersed in water as described in the preceding paragraph. Acatalyst is then added to the water and the shells formed around the oilby interfacial polymerization of the monomer.

Solid lubricants may also be encapsulated mechanically. For example,refrigerated particles of lubricant may be exposed to heated vapors ofencapsulating material in an evacuated system, the vapors condensingaround the particles. Particles may also 'be encapsulated in afilm-forming material by simultaneously passing the material andparticles through orifices and into a film-hardening bath.

My invention is further illustrated in the attached drawings in which:

FIGURE 1 is a view in perspective of a grinding wheel illustrating myinvention;

FIGURE 2 is a greatly enlarged cross-section of the wheel shown inFIGURE 1 taken along the section line 2-2;

FIGURE 3 is a view in cross-section of a coated abrasive sheet materialembodying my invention; and

FIGURE 4 is a cross-sectional view of a spherule of the type I employ inmy invention.

As shown in FIGURES 1 and 2, solidified resinous material 11 bondsabrasive grains 12 firmly in position at the radially outer portion ofthe wheel. Contained within resinous material 11 are a large number ofspherules 14 and, optionally, filler particles 13, which may be, forexample, graphite, calcium carbonate or similar material.

Turning now to FIGURE 3, flexible backing material 31 is provided with amake adhesive 32 in which are embedded abrasive granules 33. Overlyingmake adhesive 32 and abrasive granules 33 is size adhesive 34,distributed within which are lubricant-containing spherules 14. Althoughit is possible to distribute these spherules throughout the makeadhesive as well as the size adhesive, it has been found unnecessary todo so, and, further, such action may tend to weaken the make coatunnecessarily.

In FIGURE 4, spherule 14 comprises rupturable shell 15 and nucleus 16,the latter constituting the grinding aid.

My invention will be further illustrated by the following non-limitingexamples in which all parts are by weight unless otherwise indicated.

EXAMPLE 1 Preparation of lubricant-filled spherules A precondensate isformed by blending 6 moles of 37% formaldehyde in Water and 4 moles ofurea, adding triethanolamine to render the system alkaline, and heatingat 70-80 C. for 1 hour. The system is then diluted with water and acidadded to lower the pH to about 2-4. The system is continuously agitatedand reprocessed SAE motor oil added slowly; agitation is continued forabout Manufacture of grinding wheel The following materials weredirectly loaded into a cylindrical mold having a diameter of 8 inchesand a width of /2 inch:

Parts Grit aluminum oxide 278.4 Graphite, medium particle size 20.8

50-100 micron urea-formaldehyde spherules containing reprocessed SAE No.10 oil, prepared as described above 10.8

The mold was rotated about its axis at 500 r.p.m. to distribute thesolid materials, after which the following were added to the rotatingmold:

Parts DEN 438 resin 86 Methylene dianiline 24 The speed of rotation wasthen increased to 3000 r.p.m. and a 300 F. oven placed over the rotatingmold for 45 minutes. The wheel was then removed from the mold andpostcured 4 hours at 400 F. Rim thickness of the finished wheel was 1%inches.

The spherules employed in this example consist of 70% oil and 30% shellby weight, the total shell thickness being on the order of 1 micron. DEN438 is a polyfunctional epoxy novolac resin available from the DowChemical Company and having a molecular weight of 6 00, an epoxideequivalent weight of 176, and the following idealized formula:

The wheel of this example was used to grind a fiat tool steel platehaving a Rockwell C hardness of 55-60, traversing the plate incross-feed increments of 0.250 inch with 0.001 inch of down-feed. After30 passes, the wheel had cut 198 grams of steel, while a commercialvitrified wheel had cut only 186 grams of steel in the same length oftime. No burning or discoloration of the steel plate was evident witheither wheel. Conventional resin bonded grinding wheels are generallyunsatisfactory for this operation because of localized overheating ofthe workpiece. Based on total volume, the wheel of this examplecontained approximately 11.7% encapsulated grinding aid, i.e.,approximately 9% oil.

EXAMPLE 2 To a 14 inch diameter x 1 inch Wide rotating cylindrical moldwas added 850 grams of Epon 828 epoxy resin catalyzed with 18%N-aminoethyl piperazine (NAEP). The speed of rotation was then increasedto 1000 r.p.m., and the following materials added:

Parts Grade 600 aluminum oxide particles 731 Graphite, medium particlesize 222 50-100 micron urea-formaldehyde spherules of the type describedin Example 1 222 The speed of rotation was then increased to 1500r.p.m., an oven placed over the mold and the resin allowed to precurefor 45 minutes at 190 F. The wheel was then removed from the mold andcured for 2 hours at 250 F.; rim thickness was 2 inches.

Epon 828, available from the Shell Chemical Company, consistsessentially of the diglycidyl ether of Bisphenol A, having a viscosityof -160 cps. at room temperature and a molecular Weight of -192 perepoxy equivalent.

Based on total volume, the wheel of this example contained 14.0%aluminum oxide granules, 7.7% graphite, 18.8% encapsulated oil, and59.9% resin binder. This wheel was useful in polishing operations, whereit cut uniformly and smoothly with less tendency to burn than anidentical wheel containing no encapsulated oil.

, EXAMPLE 3 Into an 8 inch diameter x 1 inch wide compression mold,haivng a 1% inch diameter bore were placed the following ingredients:

The mold was subjected to a pressure of 12,000 p.s.i. at a temperatureof 300 F. and 30 minutes, after which the molded wheel was removed andcured for two additional hours at 350 F.

EXAMPLE 4 The following components were mixed together and thencentrifugally formed into a wheel as in Example 1:

- 7 Parts 78:22 DEN 438:methylene dianiline 21.4 Oil-containing capsulesas in Example 1 2.9 Grade 24 aluminum oxide particles 75.7

The finished wheel, having a rim thickness of 1% inches was tested inthe snagging of mild steel. Both the rate of cut and the tendency toresist burning were significantly better than for a control wheelcontaining no encapsulated oil. The wheel of this example contained45.5% resin, 7.7% encapsulated oil, and 46.8% abrasive granules byvolume.

EXAMPLE 5 Two wheels, A and B, were made up according to the compositionand procedure of Example 1, the only diiference being that the capsuleswere replaced in wheel A with 11.7 volume percent of 20-60 micronureaformaldehyde spherules containing Excelene NF and in Wheel B with12.8 volume percent of 30-80 micron urea-formaldehyde capsulescontaining *Excelene NF. (Excelene NF is a chlorinated mineral oil,particularly recommended as an extreme pressure lubricant.) Whensubjected to the test described in Example 1, Wheel A had a cut ratingof 105% compared to a conventional vitreous wheel, while Wheel B had acut rating of 117%. It is believed that the superior performance ofWheel B stems from the fact that the relatively greater quantity andavailability of the oil contained in each capsule.

EXAMPLE 6 A wheel identical to that of Example 1 was prepared, with thesingle difference that the urea-formaldehyde capsules had an averagediameter of 75-200'microns. When subjected to the test described inExample 1, the cut rating of this wheel was approximately 103%; it isbelieved that the rating was depressed by the comparative fragility oflarger capsules and their tendency to rupture prematurely duringformation of the wheel. Such occurrences may be minimized by increasingeither the thickness or the toughness of the capsule shell.

EXAMPLE 7 A conventional Grade 46 vitreous bonded grinding wheel wasweighed, placed in a Buchner funnel, and a vacuum of approximately 20mm. of mercury applied. A slurry of 20% encapsulated oil (as describedin Example 1) and 80% water was poured over the wheel in three separateapplications. The wheel was then removed from the funnel, dried 12 hoursat F., and weighed again, an increase of 1% being noted. When the wheelWas broken and examined under a microscope it was found thatoil-containing spherules were uniformly distributed throughout. Withsmaller capsules and/or greater vacuum, the concentration of oil in thewheel can be increased.

EXAMPLE 8 A coated abrasive product having a starchand gluefilled jeanscloth backing was coated with a glue make adhesive in the conventionalmanner and a standard quantity of Grade 150 aluminum oxide particlesapplied. The product was then sandsized with a basecatalyzedphenol-formaldehyde resin, the sole deviation from standard practicebeing the inclusion of 16% by weight (21% by volume) of 50-100 micronureaformaldehyde spherules' containing a proprietary lubricant (MyersMiracle Oil), and the resultant coated abrasive material cured. A 4 inchx 84 inch belt was formed from this material and evaluated on analuminum sanding test. After 30 minutes the belt had cut 261 grams,while a conventional belt (i.e., identical except for the absence ofencapsulated oil) out only 205 grams under the same test conditions.Tendency for the aluminum to load the surface of the belt of thisexample was significantly lower than for the control.

EXAMPLE. 9

To a 24-inch x 2-inch centrifugal mold were added the followingmaterials:

Parts Grade 16 aluminum oxide 78 78:22 DEN 438:methylene dianiline 19.850-100 micron urea-formaldehyde capsules containing SAE 20 oil 2.2

The wheel was precured for 45 minutes at 300 F. while rotating the moldat 600 r.p.m. and then removed from the mold and cured an additional 5hours at 300 F. The finished wheel, having a rim thickness of 6 inches,contained 50.2% abrasive grains, 43.3% resin, and 6.5% encapsulated oilby volume.

When tested on a snag grinder driven at 9500 surface feet per minute,the wheel of this example showed a ratio of lbs. malleable iron removedto cubic inches: wheel loss of 1.26, while a conventional resinoid wheel(of the type recommended for and commonly used in this operation) had aratio of less than 1.0.

EXAMPLE 10 To a 12 inch x 1 inch mold were added the followingmaterials:

The wheel was precured by heating for 30 minutes at 300 F. whilerotating at 2200 r.p.m., after which it was removed from the mold andpostcured for one hour at 300 F. Rim thickness was 2% inches.

Aroclor 1248 is a polychlorinated polyphenyl, yellowtinted oilywater-insoluble liquid having a specific gravity of about 1.45 and adistillation range of 330-370 C. frequently used in cutting oil; it isavailable from the Monsanto Chemical Company.

In titanium snagging operations, the wheel of this example cut 10.0grams of titanium in one minute, with a wheel loss of 32 grams. N0 undueheat was generated. In contrast, the commercial resin bonded wheelordinarily recommended for such operations out only 1 gram of titaniumwith 1 gram of wheel loss under identical conditions; when using thiscommercial wheel the workpiece became red hot and supported combustion.

EXAMPLE 11 Preparation of paraffin beads One gallon of tap water washeated to 65 C. in a 2 /2 gallon stainless steel beaker and 2 grams ofliquid detergent (Lever Brothers DW-300) added. The solution was stirredrapidly with a propeller mixer and 120 grams of melted parffin slowlyadded. The resultant dispersion was then quenched by adding 1 gallon ofice water, stirred for several additional minutes, and the water removedby suction filtering.

Encapsuation of paraffin beads To a stainless steel beaker were added440 grams of a 37% aqueous solution of formaldehyde, 164 grams of urea,and 3.2 ml. of a 25% (volume) solution of triethanolamine in water. Thereaction mixture was stirred rapidly for 1 hour at 70 F., after which800 ml. of cold tap water was added to form a urea-formaldehyde polymerstock solution.

To a stainless steel beaker containing 350 grams of theurea-formaldehyde polymer stock solution was added 2 ml. of a 25 :75volume blend of concentrated HCl:H O while stirring rapidly. Stirringwas continued, and 120 grams of paraflin wax globules added, after whichan additional 2 m1. of HCl:H O solution was added, temperature beingmaintained below 30 C. at all times. After 20 minutes of stirring, 100ml. of water was added and the temperature raised to 30 C. Stirring wascom tinned, the temperature being maintained at 30 C. for 1 hour, 35 C.for 2 hours, and 40 C. for 2 hours. The mixture was then neutralized topl-I7 by adding a dilute solution of sodium bicarbonate,suction-filtered, washed with water and dried. Average capsule diameterwas approximately 50-100 microns.

Manufacture of grinding wheel A blend of 73.8 parts by weight Epon 828,16.2 parts by weight NAEP, and 10.0 parts by weight encapsulatedparaflin was prepared, and 230 grams thereof introduced into an 8 inchdiameter x /2 inch wide mold spinning at 475 r.p.m. To the mold was thenadded 640 grams of Grade 46 aluminum oxide and the speed of rotationincreased to 2,000 r.p.m. After 1 hour the cured wheel (containing, byvolume, 50,8% cured resin, 6.7% encapsulated paraffin, and 42.5%abrasive grain) was removed from the mold and postcured 16 hours at 130F. When evaluated in the grinding of tool steel having a Rockwell Chardness of 60, this wheel caused noticeably less burning of theworkpiece than did a wheel which was identical except for omission ofthe encapsulated paraffin.

Although the foregoing examples are by no means exhaustive, it isbelieved that they suffice to show the nature of this invention. Noattempt has been made to provide specific examples for all thevariations which have been found effective. For example, it has beenfound that the particular bonding resin is not critical, assuming it hassufiicient strength to perform in that capacity. Thus, such materials aspolyurethanes, styrene-crosslinked polyesters, mixtures of monoanddi-furfuryl acetone, and similar bonding materials have been found tofunction effectively. Likewise, there has been no exhaustive attemptmade in this application to provide specific examples directed to allthose grinding aids which function effectively. Many of these arewell-known in the art, for example, chlorinated naphthalene, mineraloil, kerosene, and sulfurcontaining oils. It will also be apparent thatcertain adjustments in the composition employed should be made dependentupon the nature of the workpiece, the severity of the grindingoperation, the rate of cut desired, and

so on.

What is claimed is:

1. In a coated abrasive article comprising a flexible backing, a makeadhesive firmly bonded to one surface of said backing, abrasive grainsembedded in said make adhesive, and a sandsize overlying said grains andanchoring them firmly in position, the improvement which comprisesincluding in said sandsize a multiplicity of small hollowurea-formaldehyde or gelatin spherules having a thin shell whichcompletely surrounds a lubricant and which is distinguishable from saidsandsize adhesive, whereby the shells normally prevent contact betweensaid grinding aid and said sandsize but rupture under abradingconditions to release said lubricant.

2. The abrasive article of claim 1 in which said sandsize adhesiveconsists essentially of a phenol-formaldehyde resin and said lubricantis a lubricating oil.

3. In a circumferentially uniform accurately balanced molded rotativeabrasive article comprising a permanently hardened epoxy resin annuluswhose radially outer portion is filled to a substantial depth withabrasive grain and whose radially inner portion is devoid of abrasivegrain, the improvement which comprises including in said radially outerportion finely divided graphite and a mul tiplicity of small hollowspherules 5-500 microns in diameter having a thin urea-formaldehydeshell which completely surrounds a lubricant said spherules constitutingup to 40% by volume of the portion of said article exclusive of abrasivegrains, whereby the shells normally prevent contact between saidgrinding aid and the resin in said radially outer portion of theresinous annulus but rupture under grinding conditions to release saidgrinding aid.

4. An abrasive article comprising abrasive granules and a hardenedorganic binder therefor, said binder containing a multiplicity of smallclosed hollow spherules having a thin urea-formaldehyde or gelatin shellwhich completely surrounds a lubricant andwhich is distinguishable fromsaid binder, whereby said shells normally prevent contact between saidlubricant and said binder but rupture under grinding conditions torelease said lubricant.

5. The abrasive article of claim 4 wherein the thinshelled spheruleshave an average diameter in the range of 5-500 microns.

6. The product of claim 4 wherein the article is an abrasive wheelstructure.

7. The product of claim 4 wherein the lubricant is hydrocarbon oil. I

8. The product of claim 4 wherein the lubricant is paraffin.

References Cited UNITED STATES PATENTS 1,325,503 12/1919 Katzenstein51295 1,573,061 2/1926 Hartmann 51295 1,900,430 3/1933 Daniels 51-2951,986,849 1/1935 Pohl 51296 2,806,772 9/ 1957 Robie 51296 2,862,80612/1958 Nestor 51-298 2,986,455 5/ 1961 Sandmeyer 51-296 DONALD J.ARNOLD, Primary Examiner U.S. C1. X.R. 51 29s, 305, 306 y

